Add command_prelude module (#12291)

# Description
When implementing a `Command`, one must also import all the types
present in the function signatures for `Command`. This makes it so that
we often import the same set of types in each command implementation
file. E.g., something like this:
```rust
use nu_protocol::ast::Call;
use nu_protocol::engine::{Command, EngineState, Stack};
use nu_protocol::{
    record, Category, Example, IntoInterruptiblePipelineData, IntoPipelineData, PipelineData,
    ShellError, Signature, Span, Type, Value,
};
```

This PR adds the `nu_engine::command_prelude` module which contains the
necessary and commonly used types to implement a `Command`:
```rust
// command_prelude.rs
pub use crate::CallExt;
pub use nu_protocol::{
    ast::{Call, CellPath},
    engine::{Command, EngineState, Stack},
    record, Category, Example, IntoInterruptiblePipelineData, IntoPipelineData, IntoSpanned,
    PipelineData, Record, ShellError, Signature, Span, Spanned, SyntaxShape, Type, Value,
};
```

This should reduce the boilerplate needed to implement a command and
also gives us a place to track the breadth of the `Command` API. I tried
to be conservative with what went into the prelude modules, since it
might be hard/annoying to remove items from the prelude in the future.
Let me know if something should be included or excluded.

crates/nu_plugin_formats/src/from/eml.rs

@@ -1,14 +1,13 @@
+use crate::FromCmds;
 use eml_parser::eml::*;
 use eml_parser::EmlParser;
-use indexmap::map::IndexMap;
+use indexmap::IndexMap;
 use nu_plugin::{EngineInterface, EvaluatedCall, SimplePluginCommand};
-use nu_protocol::LabeledError;
 use nu_protocol::{
-    record, Category, PluginExample, PluginSignature, ShellError, Span, SyntaxShape, Type, Value,
+    record, Category, LabeledError, PluginExample, PluginSignature, ShellError, Span, SyntaxShape,
+    Type, Value,
 };
 
-use crate::FromCmds;
-
 const DEFAULT_BODY_PREVIEW: usize = 50;
 pub const CMD_NAME: &str = "from eml";
 

crates/nu_plugin_formats/src/from/ics.rs

@@ -1,14 +1,12 @@
-use ical::parser::ical::component::*;
-use ical::property::Property;
-use indexmap::map::IndexMap;
+use crate::FromCmds;
+use ical::{parser::ical::component::*, property::Property};
+use indexmap::IndexMap;
 use nu_plugin::{EngineInterface, EvaluatedCall, SimplePluginCommand};
 use nu_protocol::{
     record, Category, LabeledError, PluginExample, PluginSignature, ShellError, Span, Type, Value,
 };
 use std::io::BufReader;
 
-use crate::FromCmds;
-
 pub const CMD_NAME: &str = "from ics";
 
 pub struct FromIcs;

crates/nu_plugin_formats/src/from/ini.rs

@@ -1,10 +1,9 @@
+use crate::FromCmds;
 use nu_plugin::{EngineInterface, EvaluatedCall, SimplePluginCommand};
 use nu_protocol::{
     record, Category, LabeledError, PluginExample, PluginSignature, Record, ShellError, Type, Value,
 };
 
-use crate::FromCmds;
-
 pub const CMD_NAME: &str = "from ini";
 
 pub struct FromIni;

crates/nu_plugin_formats/src/from/vcf.rs

@@ -1,13 +1,11 @@
-use ical::parser::vcard::component::*;
-use ical::property::Property;
-use indexmap::map::IndexMap;
+use crate::FromCmds;
+use ical::{parser::vcard::component::*, property::Property};
+use indexmap::IndexMap;
 use nu_plugin::{EngineInterface, EvaluatedCall, SimplePluginCommand};
 use nu_protocol::{
     record, Category, LabeledError, PluginExample, PluginSignature, ShellError, Span, Type, Value,
 };
 
-use crate::FromCmds;
-
 pub const CMD_NAME: &str = "from vcf";
 
 pub struct FromVcf;